Shareholders' Equity - Components of Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Opening balance	$ (45,394)	$ (42,484)
Other comprehensive income (loss) before reclassification	22,687	12,702
Amounts reclassified from accumulated other comprehensive loss	1,134	130
Other comprehensive income, net of tax	23,821	12,832
Ending balance	(21,573)	(29,652)
Securities Available for Sale and Transferred Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Opening balance	(17,394)	(11,003)
Other comprehensive income (loss) before reclassification	23,507	12,260
Amounts reclassified from accumulated other comprehensive loss	191
Other comprehensive income, net of tax	23,698	12,260
Ending balance	6,304	1,257
Defined Benefit Pension Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Opening balance	(27,840)	(31,617)
Other comprehensive income (loss) before reclassification		1,050
Amounts reclassified from accumulated other comprehensive loss	844
Other comprehensive income, net of tax	844	1,050
Ending balance	(26,996)	(30,567)
Cash Flow Hedge Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Opening balance	(160)	136
Other comprehensive income (loss) before reclassification	(820)	(608)
Amounts reclassified from accumulated other comprehensive loss	99	130
Other comprehensive income, net of tax	(721)	(478)
Ending balance	$ (881)	$ (342)